The present invention is directed to a spark gap and more particularly the present invention is directed to a spark gap having enhanced thermal dissipation for the prevention of open circuit formation in high voltage applications.
Silicon integrated circuits are moving inexorably to finer geometries and higher frequencies, use of these circuits is also expanding into new areas requiring improved performance. One of the most important of these new areas is high voltage.
In the art presently, a problem exists, where circuit operating voltages are well below the required electrostatic discharge protection level and integrated diodes that have suitable breakdown voltages are often unavailable.
A further complication in higher voltage applications relates to the concomitant increase in the amount of energy that must be dissipated in the diode with increasing voltage.
In view of the inherent complications in the art, high voltage integrated circuits have not yet reached maturity.
Over the years, since the invention of integrated circuits, a greater number of high voltage circuit functions have been integrated into the silicon integrated circuit. Prior to the advent of this incorporation, the high voltage circuit functions were implemented with discrete components or designed into hybrid modules. These two technologies proved to be impractical from a cost effectiveness point of view for a given circuit function.
In principle, a simple spark gap could be used to provide protection for high voltage integrated circuits especially as it can hold off high voltages in either direction. A spark gap can be made to operate at less than 1000V. The two problems to be solved are how to safely absorb the increased energy dissipation and how to reduce the voltage.
The present invention seeks to overcome the limitations in the art with respect to voltage handling capacity and thermal dissipation.
By employing the technology of the present invention, it is possible to reduce the dissipation problem by making the active part of the spark gap large so that the heat is dissipated over a larger area, causing a much smaller rise in temperature. However, without other measures the size of the device needed would be inconveniently large.
The present invention solves this problem by making use of poly silicon as the spark gap material so that the dissipation problem is greatly reduced. The higher melting point of poly silicon suppresses open circuit formation and reduces the probability of conductive paths being formed out of evaporated material.
In one object of one embodiment of the present invention, there is provided a spark gap assembly suitable for use in an integrated circuit, comprising:
a first at least partially conductive electrode;
a second at least partially conductive electrode, the first electrode and the second electrode in spaced relation;
a first conductive layer overlying the first electrode and a second conductive layer overlying the second electrode;
a spark gap formed between the first conductive layer and the second conductive layer;
a plurality of discrete resistors in electrical communication with each layer proximate the gap; whereby the resistors absorb energy and limit the energy dissipated in a spark discharge in the gap.
The discrete resistors may comprise any suitable material capable of functioning as a resistor. Suitable examples include poly silicon, refractory metal, high melting point alloys.
According to another object of one embodiment of the present invention, there is provided a spark gap assembly suitable for use in an integrated circuit, comprising:
a hermetically sealed package, the package containing:
a first at least partially conductive electrode insulated portion having a conductive portion and an insulated portion;
a second at least partially conductive electrode having a conductive portion and an insulated portion, the first electrode and the second electrode in spaced relation and defining a spark gap therebetween; and
a plurality of resistors in electrical communication with each the electrode and the spark gap, whereby electrical current between electrodes is divided by the resistors for reducing the thermal energy dissipated in a spark discharged in the gap.
As alternatives, a metal with a higher melting point than aluminum instead of poly silicon could be used.
Any layer of poly silicon or any conductive layer with a sufficiently high melting point could be used for the spark gap structure.
The inventions disclosed herein may be applied to any integrated circuit which requires protection at a high voltage or to any sort of integrated circuit, particularly as it uses only conductive layers that are common to any integrated circuit (e.g. MOS, III/V, silicon carbide, bipolar).
It is possible that the application may be found outside integrated circuits, where very finely defined spark gaps are needed.
Micro mechanical integrated circuits is also emerging technology that is due to discover ESD damage. These tiny components will be very susceptible to ESD, but in many cases there will be no electronic circuitry to provide protection diodes. It would be simple and cost effective to integrate spark gaps into these devices and, if necessary, introduce an special gas at the required pressure.
Having thus generally described the invention, reference will now be made to the accompanying drawings illustrating preferred embodiments.